Indian Ocean countries and international aid agencies are putting together what the United Nations says may be the largest relief operation the world has ever seen in response to Sunday's earthquake and tsunamis. The task is especially challenging in smaller countries such as Sri Lanka where the gigantic waves claimed the most victims.

From India to Indonesia, governments and volunteers have begun distributing food and clean water to hundreds of thousands of people sheltering in schools, temples and public buildings.

For many desperate survivors, aid has been slow in coming. Some countries face shortages of supplies, others need trucks and ambulances to ferry the injured and aid. Still others must repair broken roads and telecommunications to reach jungle villages and remote islands.

Alan Bradbury at the Federation of Red Cross and Red Crescent Societies in South Asia says the geographic reach of the disaster poses a challenge on a scale never seen before. Sunday's earthquake and tidal waves killed tens of thousands of people from Indonesia to East Africa.

"It is a massive disaster. I think I can't emphasize that too much," he said. "It is the extent of the area that has been affected, it is quite unprecedented. The needs are clearly much, much greater than we had initially estimated."

At least 11 countries in Asia and Africa are affected - the worst hit are Sri Lanka, India, Indonesia and Thailand.

The United Nations says the relief operation will cost many billions of dollars. The Red Cross is already planning to triple its initial call for $6.5 million. Assessments of needs are still being made.

Aid agencies say in the coming weeks people will need food, clean water, clothes, blankets and medicines. In the long run, they need help to rebuild flattened homes and shattered lives.

In Sri Lanka, roads are jammed with dozens of trucks loaded with food and water packed by volunteer groups and local residents. But that is barely enough to cope in a country where more than one million out of its population of 19 million is now homeless. Some of the first relief planes from overseas are heading to the island.

Authorities in smaller countries such as Sri Lanka and the Maldives say they are struggling to cope with the disaster.

The deputy director of health services in the Maldives, Sheena Moosa, says the government is unable to meet the needs of thousands of people washed out of their homes.

"We do not have enough personnel to go and deliver [supplies]," she said. "And there's diarrheal disease outbreak occurring in these sites. We do not have equipment to attend to the major injured."

In Indonesia, the government has allowed U.N. staff access to Aceh province, where foreign aid workers had been barred. The U.N. workers will provide relief to about half a million people in a province that already had been battered by a separatist insurgency.

In Thailand, a naval ship headed to the devastated resort island of Phuket to attend to the many injured people.

In India, Oil Minister Mani Shankar Aiyer is supervising relief operations. He says the focus will be on rebuilding the hundreds of fishing communities that bore the brunt of the disaster.

"The highest priority has to be given to restoring the livelihood of the fishermen community. So that means boats, that means nets, that means enabling them to get back to work as soon as possible," he said.

Countries from around the world have stepped in to help, pledging everything from money to plastic sheets and tents. Governments have pledged nearly $70 million in initial aid. But coordinating the relief operations could stretch the resources of the battered countries and aid agencies.